Tuesday, August 7, 2007

PS 32-159: Is anyone home? The effect of banner-tailed kangaroo rat (Dipodomys spectabilis) mound occupancy on reptile diversity

Shawn B. Whiteman, Hollins University and Andrew J. Edelman, University of New Mexico.

Banner-tailed kangaroo rats (Dipodomys spectabilis) are considered a keystone species in desert grasslands of the southwestern U.S. These kangaroo rats build conspicuous burrow systems (mounds) consisting of raised areas 30-60 cm high and up to six m in diameter, which house a cache of seeds. Reptile and invertebrate diversity is higher on kangaroo rat mounds than in surrounding grassland; however, whether species diversity differs between occupied and unoccupied mounds is unknown. In order to compare the effect of the presence of a kangaroo rat on reptile populations, we visually surveyed reptiles found at occupied mounds, unoccupied mounds, and randomly chosen non-mound sites at the Sevilleta National Wildlife Refuge, New Mexico. In order to evaluate factors at mounds and non-mound sites that contribute to reptile population differences, we compared arthropod populations at a subsample of mounds and non-mound sites using pit traps.  We also assessed vegetation cover at all mounds and non-mound sites. Occupied mounds had greater overall reptile abundance, reptile species richness, and reptile abundance per survey than unoccupied mounds, and both occupied and unoccupied mounds had greater overall reptile abundance, reptile species richness, and reptile abundance per survey than non-mound sites. Occupied and unoccupied mounds did not vary in vegetation cover or arthropod abundance, but had lower vegetation cover and higher arthropod abundance than non-mound sites. This indicates that the presence of kangaroo rats positively affects reptile abundance and species richness either directly or indirectly through a factor other than vegetation cover and arthropod abundance.

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